The invention relates to a connecting device for power semiconductor modules having a substrate and a housing with compensation for mechanical stresses which are caused by the effects of different material characteristics of components when a temperature change occurs.
Power semiconductors have been increasingly used in recent years in automobile electronics, energy management and, increasingly, for industrial drive and automation technology as well. As a rule, those power semiconductors are combined to form modules, which are matched to customer-specific requirements.
In such power semiconductor modules, individual electronic components are generally soldered to a ceramic substrate. In some cases, the ceramic substrate is in turn soldered to a baseplate (heat sink). That ensures adequate dissipation of heat from the electronic components during operation. An example of a bipolar transistor module with an integrated gate (IGBT) is described in detail below with reference to FIG. 5 and is disclosed in an article entitled xe2x80x9cZuverlxc3xa4ssigkeit von Al-Dickdraht-Bondverbindungenxe2x80x9d, [Reliability of Aluminum Thick-Wire Bonded Connections] ISHM Conference Munich 1996, Auerbach, Schwarzbauer, Lammers, Lenninger, Sommer.
In order to make it possible to ensure reliable bonded connections in such a power semiconductor module, the connections have to be fixed in position by complex workpiece supports during the soldering process. That means that the production process is complex, and is subject to the influences of faults. Furthermore, when using such aluminum bonded connections, a maximum permissible current intensity is limited by a bonding wire length and a bonding wire diameter.
It is accordingly an object of the invention to provide a connecting device for power semiconductor modules with compensation for mechanical stresses, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which makes direct contact with connections of a power semiconductor on a substrate, in order to compensate for thermally dependent mechanical stresses using simple measures.
With the foregoing and other objects in view there is provided, in accordance with the invention, a connecting device for power semiconductor modules, comprising a sleeve connected to a substrate of a power semiconductor module. The sleeve has a region with a given very small diameter. A wire pin is provided for insertion into the region of the sleeve during operation to form an electrical connection for a board. The wire pin has a diameter greater than the given diameter for clamping the wire pin upon insertion in the region.
In accordance with another feature of the invention, in order to improve insulation, the housing is formed of plastic.
In accordance with a further feature of the invention, the sleeve is soldered to the substrate. In this context, it is feasible for the sleeve to be soldered to the substrate together with further electronic components during one furnace run. This advantageously allows the power semiconductor module to be produced efficiently.
In accordance with an added feature of the invention, in order to prepare for soldering, the substrate is provided with surfaces which can be wetted and surround an etched trench disposed in the surface of the substrate. Furthermore, the substrate is printed with a paste solder. Before the furnace run or the soldering process, the sleeve is placed on the paste solder. The subsequent flowing of the paste solder during the furnace run results in surface-tension forces being produced between the surfaces which can be wetted and the sleeve. Those forces center the sleeve with respect to the etched trench. This allows the sleeve to be aligned on the substrate in a very simple manner and with very accurate position and orientation tolerances, thus further simplifying the production of the power semiconductor module.
As mentioned above, the wire pin is introduced into the sleeve which is connected to the substrate. The sleeve and the wire pin thus form a two-part plug system, which replaces the previously used bonded connections, that were described initially, between the substrate and the board. The wire pin is clamped firmly in the sleeve by the advantageous shaping of the sleeve.
In accordance with an additional feature of the invention, the wire pin can still be moved axially in the sleeve under the influence of external force. This refinement advantageously makes it possible, in a state in which an end of the wire pin that is opposite the sleeve is connected to a board and the power semiconductor module is fitted to this board, for disadvantageous mechanical stresses caused by temperature changes to be dissipated directly once again. A further advantage of this exemplary embodiment results from the fact that the wire pin can still be soldered until it is fitted on the board, since the wire pin is not introduced into the sleeve until after the furnace run.
A further advantage of the two-part plug system including the sleeve and the wire pin for electrical connection of the substrate to the board is furthermore that the maximum permissible current intensity between the substrate and the board is greater than with the previous bonded connections. The wire diameter and bonding wire length, which in the past have been critical parameters in terms of current capacity, are of only secondary importance with the plug system according to the invention.
In accordance with yet another feature of the invention, both the sleeve and the wire pin are formed of tinned copper or copper alloys, thus ensuring that these components can be soldered well. In this context, appropriate material selection is generally required for the sleeve and the wire pin in order to avoid damaging contact corrosion, such as that which occurs between iron and copper.
In accordance with yet a further feature of the invention, the sleeve includes a bottom section and a casing section, with the casing section in the simplest case having an essentially cylindrical shape, for example. This ensures that the wire pin is clamped adequately even without any need to comply with exact tolerances on the cylinder diameter. In order to improve the capability of inserting the wire pin, it is conceivable for the wire pin to be provided on its end section with a chamfer, which is used as an insertion incline. The two-part plug system mentioned above can thus advantageously be ensured even by this simple exemplary embodiment.
In accordance with yet an added feature of the invention, the casing section of the sleeve has a funnel shape, thus further simplifying the insertion of the wire pin. As an alternative thereto, in this exemplary embodiment, insertion inclines can also be provided on the wire pin. When configured in the shape of a funnel, the casing section has arms between which slots are formed for the situation where the substrate is subjected to a washing process after soldering. In this case the slots advantageously ensure that flux residue can escape from the interior of the sleeve, and can thus be removed without leaving any residue.
In accordance with a concomitant feature of the invention, the housing of the power semiconductor module is filled with silica gel to insulate the components. The slots mentioned above in this case allow air to escape from the silica gel in the region of the sleeve, thus ensuring reliable insulation.
The connecting device according to the invention is assembled by placing at least one sleeve on a paste solder which has been applied to the substrate, by heating the substrate together with the sleeve in order to solder the sleeve to the substrate, and by introducing a wire pin into the respective sleeve. An electrical connection is produced between the power semiconductor module and a board through the wire pin.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a connecting device for power semiconductor modules with compensation for mechanical stresses, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention as well as within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.